Furnace



Jul 23, 1929.-

rummca ori inal File'aocz. so, 1925 Patented July 23, 1929.

UNITED STATES PATIENT OFFICE.

IRVING B. SMITH, OF AKBLEB, PENNSYLVANIA, AS BIGNOR TO LEEDS & NORTHRUP COMPANY, OF I'HILADELPHIA, PENNSYLVANIA, A' CORPORATION 01' PENNSYL- VANIA.

FURNACE.

Original application flied October 30, 1925, Serial. Io. 65,715. Divided and this 8, 1988. Serial No. 858,488.

My invention relates to heating apparatus, as furnaces, and more particularly to electrically heated furnaces utilizable for various purposes, and particularly for heat treatment of steel and kindred materials, as, for many ple, for drawing or tempering steel or the like.

In accordance with my invention, to render more uniform the temperature throughout the heating chamber, and more particularly throughout the contents thereof treated therein, circulation, and particularly forced circulation, in either direction, of the air or gas, more particularly within the furnace is effected in a path or circuit including a work-.

containing chamber, and an air heating chamber, more particularly an outer chamber of said furnace, preferably containing the source of heat, and suitable passages effecting communication between the chambers.

My invention resides in apparatus of the character hereinafter described and claimed. For an illustration of some of the various forms my invention may take, reference is be had to the accompanying drawings, in which:

Fig. 1 is a vertical sectional view, partly 1n elevation, of an electric furnace embodying my invention. v

Fig. 2 is a horizontal sectional view, partly in plan, on the line 22 of Fig. 1.

, Fig. 3 is a vertical sectional view of a modified form of furnace. Referring to-Figs. 1 and 2, there is shown a furnace or heat treating apparatus F, adapted for forced circulation, comprising the metal jacket or housing 1, which may be cylindrical, secured at its lower end to the bottom member 2, carried by a frame having the legs 3. Disposed within and spaced from the jacket 1 is the shell or inner lining 1, whose bottom 5 is spaced from the bottom 2 by the blocks 6, through which extend the bolts 7 which secure the member 5 and also the verti ally extending supporting members 8 to the bottom 2. Between the shells 1 and 4, and between the bottoms 2 and 5, is disposed any suitable filling 9, of refractory material of preferably low heat conductivity. The upper end of the lining 4 is secured to the annular member 10, surrounded by the ring 11 ofrefractory material, which in turn is surrounded by the brick ring 12, upon which latter rests the top annular casting 13,

application filed March w ch there is pivoted at 15 the arm 16, to which is pivoted at 17 the lid or cover member 18, which may be raised by pressing downwardly upon the lever 19, pivoted at 20 er adjacent the inner lining 4. As indi-' cated, in Fig. 2, there are two sets of resistances, each comprising a plurality of parallel connected ,resistors or resistance conductors extending vertically adjacent and insulated from the lining 4. Connections are made to the resistors through conductors having terminals in the terminal boxes 23 and 24. In thecxample illustrated, the resistance elements 21 and 22 are exposed to direct contact therewith of the air or other gas within the furnace chamber. I

Between the upper and lower rings 25 and 26 and the standards or members 8 is secured the shell or basket support 27, of sheetnietal, preferably circumferentially and vertically continuous or substantially uninterrupted by perforations or openings, to exclude radiant heat from the interior of the shell 27.

The removable basket or container for the material to be heated comprises the closed shell 28 secured at its upper end to the ring 29, having the eyes 29 for reception of crane hooks, and having the outwardly extending flange 30 resting upon the upper end of the shell 27 and members 8. At its lower end the shell 28 is secured to the spider 31.

Disposedvbelow the basket and its spider 31 and forming a bottom for the shell 27 is the conical or funnel-shaped member 32 secured upon a ring or pieces 33 secured to the members 8.

Bolted to the bottom 2 is the fan shaft bearing member 34, in which is dis osed the shaft 35, upon which is secured tiie pulley uplon which is carried the support 14, to

36 driven through belt 37 by the pulley 38 secured upon the shaft of the. electric motor M, for driving the fan or blower 39, disposed at the opening 40 at the bottom of the member 32. The bottom 5 of the inner lining 4 preferably deflects upwardly, as at 41, to

form a passage leading to the lower side of the fan 39.

In the modification illustrated in Fig. 3, the removable lid or cover 18 carries the bearing 34 .for the fan shaft 35 driven by belt 37 through pulley 36. At its lower end the shaft carries the propeller or fan 39, adj acent a-nd above which is disposed the downwardly extending air-guiding surface 41*, and beneath the fan is disposed the conical or funnel-shaped member 32 carried by the upper ring 29 of the basket or work container 28. The opening of the; member 32 is disposed adjacent the fan 39.

In both forms of my apparatus above de- 4 scribed, there .is effected forced circulation by the fan or propeller 39 through a path or in a circuit comprising .the space between the grating or spider 31. The work may be a single piece, or a plurality of pieces either carefully or symn'letrically piled within the basket or placed therein irregularly. For example, the contents of the basket maybe a plurality of gearsof steel or alloy steel to receive heat treatment of any suitable character, for example, for drawing or tempering, although it will be understood that my invention embraces heat treatment of other oby'grcts, and of other metals, or their alloys.

ith the furnace cold, it is brought rapidly to the desired temperature, as, for example, a temperature of a predetermined magnitude at which the chamber is to be maintained, by passing current through the sets of resistors 21 and 22 in parallel. The desired temperature depends upon the treatment to be effected and characteristics of the material or objects to be treated; it is well known that for annealing or hardening the temperatures are from approximately 1300 degrees F to about 1700 degrees F. while for tempering, the temperature is, in general, lower and may be from about 300 degrees F. to 1200 degrees F., more or less. During this preliminary stage of heating-the fan 39 is driven by the motor M at suitable speed,

effecting circulation of the hot gases or air dowmvardly, Fig. 1, between the shells 4 and 27, past the resistors 21 and 22, thence between the members 32 and 41 to the under side of the fan 39, which forces the air or gases upwardly through the member 32, spider 31, through the basket or shelf 28, upwardly through and between the gears 01 other pieces therein, and thence outwardly over the edge of the basket and thence downwardly again between the shells 4 and 27.

This circulation of the heated air or gas serves to maintain the temperature rise more uniform throughout the basket and its contents and serves also to expedite the rise in temperature of the furnace. After the furnace has attained desired temperature, as may be determined by the thermocouple T, connected in suitable circuit by conductors 72 and'73, or has approximated such desired temperature, the rate of heat application may be diminished, as by utilizing only asuitable part of either or both of the resistors 21 and 22, or by connecting them in series with each other. The control of the temperature of the furnace may be automatically effected by any suitable apparatus controlled by the thermocouple T, or equivalent temperature-responsive device.

By so circulating the air or gases within the furnace, greater uniformityof temperature of the work or contents 015' the basket 28 is obtained, with resultant advantage that the work or material is more uniformly heat-treated, yielding products more uniform in their characteristics as affected by the heat treatment.

The desired uniformity of temperature of' the contents of the basket is the more readily obtainable from the fact that the basket 28 or the shell 27, or both, intercept the radiant heat which would otherwise be absorbed by those parts of the contents lying adjacent the wall or shell 28, causing them locally to attain a temperature higher than is due to the heating effects of convection or conduction of or from the hot air or gases. In other words, it is preferred that the heating shall be effected substantially exclusively by convection or conduction and that heating effects due to radiant heat should be minimized.

A furnace of the character herein described is utilizable for various methods of heat treatment, including that described in The direction of circulation of the air or gas within the furnace may be reversed from time to time or periodically. as by reversing the direction of rotation of the fan or blower 39, as described and claimed in application ticularly the resistors or Serial No. 10,486, filled by ohn W. Harsch heat capacity, or small eapacity for storing heat, in the sense that they are directly or substantially directly exposed to the air or gas within the furnace, or, if embedded, the mass shall be small enough to store only relatively small amount of heat; or shall have a heat capacity which is low as compared with the heat capacity of the material or work to be heat-treated. This low heat capacity of the resistance elements 21 and 22,- or equivalent, is desirable from the standpoint of ability rapidly to change in temperature, thereby contributing, with the circulation of the air, to reduction or elimination of over-shooting of temperature either when bringing the heating chamber up todesired or control temperature, or during control of temperature after the heating chamber has been so brought up to or near the desired temperature.v

It has heretofore been proposed, as in drying systems and in systems for annealing metal, to impart heat to and absorb heat from forcibly circulated air in zones comprised in a system characterized by the fact that of the total length of the path of the circulated air the sum of the lengths of the paths in the aforesaid zones is a small fraction, occasioned by the relatively great length of air conduit comprised in the circulatory system and essential to operative intercommunieation of the zones. From such systems mine materially differs inthat the length of the circulatory path outside of the heating and treating zones is relatively short, communication between the zones is substantially immediate or direct, and of the entire length of the circulatory path the sum of the lengths of the zones is a large or major fraction,, thereby procuring the practical advantages of reduction of power consumption for foreibly circulating the air, of economy in fuel or power expended in the generation of heat, of lower cost of installation and maintenance, and of smaller space required to accommodate the system. Because of the relatively great length of the path of the circulating air in the aforesaid proposed systems, external to their air-heating and heat-absorbing zones, greater power is required for forcing the circulation of the air, and more fuel or power must be consumed in the production of the eventually essential heat because of relatively high losses by conduction and radiation.

For brevity in the appended claims, the term air is employed generically to include air, gas and vapor within the furnace or heatmg chamber.

"What I claim is:

1. furnace comprising a heating chamber, a container disposed within said chamber and spaced from the wall thereof for holding the material to be heated, a source of heat disposed in the space between said container and said wall of said heating chamber, and an air propeller within the furnace disposed adjacent neighboring ends of said container and heating chamber for circulating air through said container and the space between said container and said wall of said chamber.

2. A furnace comprising a heating chamher, a container disposed within said chamber and spaced from the wall thereof for holding the material to be heated, a source of heat disposed in the space between said container and said wall of said heating chamber, an air propeller within the furnace disposed adjacent neighborhood ends of said container and heating chamber for circulating air through said container and the space between said container and said Wall of said chamber, and a member surrounding said container between the container and the Wall of said chamber for shielding the work in said container from radiant heat from said source.

3. A furnace comprising a heating chamber, a container for the material to be heated disposed within said chamber and having its side walls spaced from the side walls of said heating chamber, an electric resistor of low heat capacity disposed in said space between the side walls of the container and said heating chamber, and a propeller within the furnace disposed adjacent the neighboring ends of said container and heating chamber for circulating air through said container and through the space between the side walls of said container and said heating chamber.

4:. A furnace comprising a heating chamber, a container for the material 'to be heated disposed within said chamber and having its side walls spaced from the side walls of said heating chamber, an electric resistor of low heat capacity disposed in said space between the side walls of the container and said heating chamber, a propeller within the furnace disposed adjacent the neighboring ends of said container and heating chamber for circulating air through said container and through the space between the side walls of said container and said heating chamber, and a'member surrounding said container and disposed betwecn it and said resistor for intercepting radiant heat from said resistor.

5. A furnace comprising a heating cham her having a bottom and a cover, a container for the material to be heated disposed in said chamber with its side walls spaced from the side walls of said heating chamber and having its ends spaced from said bottom and cover to form passages communicating with the interior of said container and with the space between the side walls of said container f amd the side walls of said heating chamber,

tween the sidewalls of said 6. A furnace comprising a heating chain-- her having a bottom and a cover, a container for the material to be heated disposed in said chamber with its side wall spaced from the side wall of said heating chamber and having its ends spaced from said bottom and cover to form passages communicating with the interior of said container and with the space between the side wall of said container and the side wall of said heating chamber, an electric heater disposed in the space between the sidewalls of said-container and said heating chamber, a propeller within said furnace disposed adjacent neighboring ends of said container and said heating chamber for circulating air through said container, said passages and the spacebetween the side vwalls of said container and said heating chamber, and a member surrounding said container and'disposed between it and said heater for intercepting radiant heat from said-heater.

7. A furnace comprising a,--heating chamher having a bottom, a removable cover, members disposed within said chamber and spaced from .the side wall thereof, a removable work container resting upon said members and having'its sidewall spaced from said side wall of said heating chamber, a heater in" the space between the side Walls of said containerand heating-chamber, said heating chamber having its ends spaced from said cover and from 'said bottom to form circulatory passages between the interior of said container and the space between the side walls of said container and said heating chamber, and apropeller within said furnace between adjacent ends of said container and said heating chamber for circulating the air through said container, said passages and the space between the side walls of said container and said heating. chamber.

8. A furnace comprising a heating chamber having'a bottom, a removable cover, members disposed within said chamber and spaced from the side wall thereof, a removable work container resting upon said members and having, its side-walk spaced from said side wall of said heating chamber, a heater in the space between the side walls of saidcontainer and heating chamber, said heating chamber having its ends spaced from sald cover and from said bottom to form circulatory passages between the'interior of said container and the space between the side walls of said container-and saidheating chamber, a prosaid heating chamber.

peller within'said furnace between adjacent ends of said container and said heating chamber for circulating air through said container,

said passages and the space between the side her, a removable container therein for the material to be heated and having its side Wall spaced from the side wall of said heating chamber, a heater in the space between said side walls, end closures for said heating chamber spaced from opposite ends of said container, apropeller disposed between one of said end closures and the adjacent end of sai container, and air-guiding members forming a passage to said propeller between the interior of said container and the space between the side walls of said container and 10. A furnace comprising a heating chamber, a removable container therein for the material to be heated and having its side Wall spaced from the side wall ofsaidheating chamber, a heater in the space between said side walls, end closures for said heating chamber spaced from opposite ends of said container, a propeller disposed between one of said end closures and the adjacent end of said container, air-guiding members forming a passage to said propeller between the interior of said container and the space between the side walls of said container and said heating chamber, and a member surrounding said container and disposed between it and said heater for shielding said container from radiant heat from said heater.

11. A furnace comprising a heating chamher having a bottom and a removable cover, I

members on said bottom extending upwardly within said chamber, a removable container for the material to be heated, meanspn the upper end of said container resting upon said members, an electric heater in the space between the side walls of said container and said heating chamber, and means forcibly circulating air through said space and said heating chamber in succession. 1

12. A furnace comprising a heating chamand spaced'therefrom, a'removable container in said shellfor holding the material to be heated, and means for forcibly circulating air through said container and the space between said shell and said heating chamber.

13. furnace comprising a heating chamher, a source of heat, a shell disposed therein 'ber, a source of heat, a shell disposed therein and spaced therefrom, a removable container in said shell forholding the material to be heated, and means for circulating air throu h said container and the space between sa d shell and said heating chamber, said shell preventing access of radiant heat to the material in said container.

14. A furnace comprising a heating chamber, a container therein spaced from the wall thereof and adapted to hold material to be heated, said container at one end communicating with the space between it and said heating chamber, and an air-circulating member disposed adjacent an opening at the other end of said container for circulating air therethrough and through the space between said container and said'chamber. 7

15. A furnace comprising a heating chamber, an electric heater disposed upon the wall thereof, a shell spaced from said Wall, a container in said shell for holding the material to behea'ted,.a member having an opening and flaring from said opening toward said container, and air-circulating means disposed at said 0 ening.

16. A urnace comprising a heating chamber, an electric heater disposed upon the wall thereof, a shell spaced from said wall, a container in said shell for holding the material to be heated, a member having an opening and flaring from said opening toward said container, air-circulating means disposed at said opening, and means on the exterior of said furnace for driving said air-circulating means.

compared with the heat capacity of the work heated within said container, said heater disposed in the space betweenthe side walls of said heating chamber and said container, and

means adjacent neighboring ends of said conchamber, means for effecting circulation of air or equivalent from said heating chamber through said container and work to affect the temperature thereof, and a second structure having sheet-like walls interposed between said heating elements and work container forming an air space between said structures whereby radiantheat from said'elements is effectively recluded to a substantial degree from affecting the temperature of the work adjacent the walls of the container.

19. A heat-treating furnace comprising a metal-heating chamber, an air-heating chamber, said chambers being in substantially direct or immediate communication at separated regions, and means forcibly circulating air through said chambers in succession.

20. A heat-treating furnace comprising a metal-heatin chamber, an air-heating chamber surrounding said metal-heating chamber and insubstantially direct and immediate communication therewith at separated re, gions, a source ofradiant heat in said airheating chamber,-means forcibly circulating air through said chambers in succession, and means shielding the metal in said metal-heating cha'mberfrom radiant heat from said source.

iavme B. SMITH. 

